For improvement in usability of car navigators and the like, various systems or interfaces enabling conversation with the user by speech have been proposed. A speech conversation system retrieves necessary information from a database storing information of a specific domain, such as route guidance, traffic information, weather information or the like, to provide it to the user. Further, a speech conversation system provided with a plurality of databases storing information of a plurality of domains, respectively, is also provided, to enable variable conversations with the user. In such a speech conversation system intended for conversations over a plurality of domains, it is necessary to select an appropriate domain in consideration of the content of the user's utterance. Various techniques for selecting a domain have conventionally been proposed, as in the following publications.
1. Makoto Nagamori et al., “A Framework for Multi-Domain Conversational Systems”, Information Processing Society of Japan, Report No. 2000-SLP-31-7, 2000
2. Nobuo Kawaguchi et al., “Design and Evaluation of A Unified Management Architecture for Multi-Domain Spoken Dialogue”, Information Processing Society of Japan, Report No. 2001-SLP-36-10, 2001
3. I. O'Neill et al., “Cross Domain Dialogue Modeling: An Object-Based Approach”, In Proc. ICSLP, Vol. I, 2004
According to the conventional techniques, however, there exist limitations such that transition of domains is permitted only after a task is accomplished, or even if the transition is permitted, it is only from the currently selected domain to the one similar to that domain. This causes an inappropriate domain in consideration of the content of the user's utterance to be selected a plurality of number of times, resulting in excessive elongation of the state with a gap in conversation between the user and the system.
In view of the foregoing, an object of the present invention is to provide a system which can advance a conversation with a user with improved capability of following the content of the user's utterance, and software which causes a computer to function as the conversation system.